This invention relates in general to screw machines for homogenizing materials of solid, liquid and pasty consistency and more specifically to homogenizing screw machines having engaging screw shafts that have screw sections and core shaft sections that mount at least one disc.
By the term homogenizing all those processes are meant hereinafter by means of which the macro- or microstructure of masses having one or several components is made more uniform, i.e. especially the processes of mixing, kneading, dispersing, emulsifying, plasticizing and the like.
Screw machines having several screw shafts of the aforesaid kind which mesh with one another and are driven in the same or opposite direction are known for processing plastics and other materials. Normally on the screw shafts of these machines several cylindrical (not circular cylindrical) annular discs are mounted alongside one another and separated from one another by means of intermediate annular discs on a core shaft section, which is contained between two screw sections serving to convey the material to be processed, said screw sections being non-rotatably connected to the core shaft section. The intermediate annular discs are necessary, since the cylindrical annular discs of screw shafts meshing with one another must be prevented from rubbing against one another as a result of uneven temperature conditions or manufacturing inaccuracies of the two screw shafts.
In the known screw machines of the type described at the beginning the annular discs of the screw shafts are safeguarded from rotating relative to the respective core shaft section in that the latter is provided with several longitudinal grooves spaced along its periphery, in which corresponding keys or internal keys of the annular discs engage. At least one of the screw sections adjacent the set of annular discs can be removed, so that it is possible to remove the annular discs from the core shaft section and replace them on the core shaft section rotated in relation to the latter and in relation to one another. By means of corresponding choice of the angular positions of the various annular discs in relation to one another and to the adjacent screw sections the duration of the stay of the material to be processed in the homogenizing zone of the screw shaft formed by the set of annular discs and the energy which is introduced in this homogenizing zone into the material to be processed can be altered and predetermined. The disadvantage in the known screw shafts constructed in the above described manner is that they must be removed from the machine in order to alter the angular positions of the annular discs, which is bothersome and time consuming, since drive means and mounting of such screw shafts must be in a position to receive and transfer considerable forces and torques and are thus constructed in such a way as to prevent simple and quick removal and installation of the screw shafts. However, since both the energy consumption and said duration of the stay should be very different depending on the product, task and process, it is desirable in order to make optimum use of the machine, energy and product that the geometry of the screw shafts be adapted to the respective requirements, which is, of course, only be carried out if this adaptation can be effected relatively quickly and simply.
A further disadvantage of the above described, known screw machines is that the design of the required intermediate annular discs depends on the respectively chosen relative angular position of adjacent annular discs if an abutting of the intermediate annular discs of a screw shaft against the annular discs of the screw shaft located opposite is to be excluded, and gaps and therefore dead zones between inactive surfaces of adjacent annular discs are to be avoided--for example, in such dead zones delicate plastics can be thermically damaged owing to the prolonged duration of the stay, and furthermore, they make the cleaning of the screw shafts more difficult when the material is being changed. Thus, the most varied shapes of intermediate annular discs are required for the known screw machines. The object of the invention was to improve the screw shafts of a screw machine of the type described at the beginning in such a way that their removal from the machine for the purpose of altering the angular position of one or several annular discs is no longer necessary. This object is fulfilled according to the invention in that the annular disc on the core shaft section of the respective screw shaft is rotatable at least in the operational direction of rotation of this screw shaft--since screw shafts for the aforesaid purposes always rotate only in a direction determined by the construction, it is adequate to ensure that the annular disc is carried along in this direction, i.e. in normal operation cannot be rotated in relation to the adjacent screw sections in a direction opposite to the operational direction of rotation. One can then readily design the construction in such a way that the annular disc can be rotated and adjusted in the operational direction of rotation of the screw shaft, i.e., in the sense of a lead, in relation to the adjacent screw section, without the screw shaft having to be removed from the machine for this purpose. Of course, the annular disc does not have to be continuously rotatable through a full 360.degree., it is sufficient for it to be displacable in certain angular steps in relation to the core shaft section. If the annular discs were now mounted in the manner known per se on the core shaft section with interposed intermediate annular discs, rotation of the annular discs would result in the occurence of dead zones between adjacent annular discs and the abutting of annular and intermediate annular discs of screw shafts located opposite one another, so that under certain circumstances the screw shafts might indeed have to be removed, particularly for cleaning purposes when the material is being changed. Thus in accordance with the invention it is further suggested that the radially overlapping annular discs of the engaging screw shafts be designed in such a way that they are provided with peripheral zones of decreased width in the overlapping region. More particularly, the annular discs should be of decreased width starting at a certain diameter, which is slightly smaller than the axial distance (practical axial distance) between the two engaging screw shafts. One can then avoid the use of intermediate discs without having to tolerate gaps and dead zones between inactive surfaces of the annular discs and the abutting of annular and intermediate annular discs of screw shafts located opposite one another Consequently, it is no longer necessary to remove the screw shafts from the screw machine.
The annular discs could be of decreased width in the peripheral zone by, for example, providing them with a triangular profile. One could also consider decreasing the width by means of a reduction at one endface only of the annular disc. However, in a preferred embodiment of the invention both sides of the annular discs are provided with shoulders in the peripheral zones thereby decreasing the width of the annular discs in this peripheral zones.
The energy introduced in a homogenizing zone to the material to be processed depends among other things on the width of the gaps between the active surfaces of annular discs meshing with one another. In order to enable easy adaptation to desired operational conditions, it is suggested in accordance with the invention that the peripheral zones of decreased width be formed by exchangeable parts. Therefore the width of the gap can be altered without removing the screw shafts, namely by opening the machine housing which is separated in a manner known per se, in order to make the annular discs accessible, whereupon the parts forming the peripheral zones of decreased width can be exchanged.
For the purpose of readjusting the annular disc or annular discs of a screw shaft the machine housing surrounding the screw shaft can, for example, be provided with an opening or can be divided in a manner known per se and designed to be pulled apart, it is, however, also possible to provide a hollow core shaft for the screw shaft and adjust the annular disc or annular discs via the core shaft cavity. Since the action of the apparatus can be changed from non feeding mode to axial forward or backward feeding mode by altering only the angle of displacement of an annular disc in relation to adjacent screw sections and/or the angle of displacement of the annular discs of a set of annular discs in relation to one another, and the duration of the stay of the material in the homogenizing zone and the amount of the energy introduced in the homogenizing zone per unit of time can thereby be preselected, the invention makes it possible to optimize the function of a screw machine in a controlled manner, e.g. by computer control, since it is no longer necessary to remove the screw shaft in order to adapt the function of the homogenizing zone to the material to be processed.
The annular discs can have any cross section differing from a circle concentric to the center of the core shaft section, but preferably they have the shape of sections of a screw. Moreover, discs which do not form a complete closed ring can, of course, also be used instead of closed annular discs.
In a first particularly advantageous embodiment of a screw shaft for a screw machine according to the invention the core shaft section is provided over its circumference with several longitudinal extending, spaced notches, in which engages at least one stop element of the annular disc being adjustable in radial direction. This stop element can be, for example, a screw bolt which is screwed through the annular disc from the outside and engages in one of the notches of the core shaft section. In order to provide for easier adjustment of the annular disc it is recommended that the core shaft section be provided with a saw tooth profile along its circumference, so that the stop element can be designed as a bolt sprung in radial direction, namely biased in a direction towards the core shaft section, and guided in the annular disc, and that the annular disc can be rotated in one direction on the core shaft section whilst it is carried along in the other direction of rotation of the screw shaft by the saw teeth of the core shaft section.
In another particularly advantageous embodiment the annular disc is clamped in axial direction between adjacent parts of the screw shaft and at least its one endface and the adjacent endface of the adjoining part have a profile extending preferably in a radial direction. If the core shaft has several annular discs, the endfaces of all these annular discs and the front sides of the screw sections facing the set of annular discs have a profile as described above, so that by shifting the screw sections in an axial direction, namely in a direction towards the set of annular discs, the annular discs can be non rotatably coupled with the screw sections, while they can be freely rotated relative to the core shaft section when the screw sections are pulled apart.
In a third, particularly preferred embodiment the annular disc is mounted on a well known annular clamping spring, which is adapted to be clamped in axial direction between parts non rotatably mounted at the screw shaft. In a set of annular discs all the annular discs are mounted on annular clamping springs well known in the art, so that when the screw sections are pulled together in a direction towards the set of annular discs the annular clamping springs are clamped in an axial direction and thereby expand in a radial direction, so that they couple the annular discs with the core shaft section by means of a frictional connection.
Finally, a further embodiment comprises a hollow core shaft section with a window, through which a pinion adjustable and lockable in relation to the screw shaft projects and engages in an internal toothing or the like of the annular disc. If, for example, the pinion is attached to an axis extending to one end of the screw shaft, the annular disc can be adjusted and locked from the end of the screw shaft.
Further features, advantages and details of the invention are disclosed in the enclosed claims, the following description and the enclosed drawings of various, preferred embodiments of screw machines in accordance with the invention.
FIG. 1 is a plan view, partly in section of a screw machine comprising two screw shafts meshing with one another and designed in accordance with the invention;
FIG. 2 is a sectional view of a larger scale than FIG. 1 of two sets of annular discs meshing with one another according to a first embodiment of the screw shafts;
FIG. 3 is a side view of one of the annular discs shown in FIG. 2;
FIG. 4a is a complete side view of a part of one of the two screw shafts shown in FIG. 1 and 2 with a set of annular discs, but where the annular discs adapt other positions in relation to one another;
FIG. 4b is a section of the screw shaft taken along the line 4b--4b shown in FIG. 4a;
FIG. 5a is an illustration of a second embodiment of a screw shaft corresponding to FIG. 4a;
FIG. 5b is a section through the second embodiment corresponding to FIG. 4b;
FIG. 6a is an illustration, partly in section, corresponding to FIG. 4a, of a third embodiment of a screw shaft;
FIG. 6b is a section through this third embodiment corresponding to FIG. 4b;
FIG. 7a is an illustration of a fourth embodiment of a screw shaft corresponding to FIG. 4a, wherein for reasons of simplicity only one single annular disc is shown;
FIG. 7b is a section through the fourth embodiment corresponding to FIG. 4b;
FIG. 8a is an illustration of a fifth embodiment corresponding to FIG. 4a, and
FIG. 8b is a section through this fifth embodiment corresponding to FIG. 4b .